The present invention relates generally to an apparatus and method for improved optical geometry for enhancement of spectroscopic detection of analytes in a sample. More particularly, the invention relates to an apparatus and method for ultrasensitive detection of prions and other low-level analytes.
A conventional method of performing laser induced fluorescence as well as other types of spectroscopic measurements such as infrared, UV-vis, phosphorescence, etc. is to use a small transparent cuvette to contain the sample to be analyzed. A standard cuvette has dimensions of about 1 cm×1 cm and is about 3.5 cm in height and sealed at the bottom. The cuvette is usually made of fused quartz or optical quality borosilicate glass, is optically polished and may have an antireflective coating. The cuvette is filled from an upper, open end that may be equipped with a stopper.
To perform a measurement, the cuvette is filled with the liquid to be investigated and then illuminated with a laser focused through one of the cuvette's faces. A lens is placed in line with one of the faces of the cuvette located at ninety degrees from the input window to collect the laser-induced fluorescence light, so as to reduce interference from the laser itself and from other noise. Only a small volume of the cuvette is actually illuminated by the laser and produces a detectable spectroscopic emission. The output signal is significantly reduced by the fact that the lens picks up only approximately ten percent of the spectroscopic emission due to solid angle considerations. This general system has been used for at least seventy-five years.
Previous developments described in U.S. patent application Ser. No. 11/634,546, filed on Dec. 7, 2006, increased the amount of output signal by approximately a factor of ten over the prior art known at the time, resulting in micromolar limits of detection of fluorescent compounds. The present invention further improves upon this technology, and may result in detection of attomolar quantities of fluorescent compounds.